86 THE TRANSFORMATIONS OF THE ANIMAL WORLD 



from an order of dogfish, the Ichfhyotomi, which 

 possess also the characteristics of the Dipneusta, 

 that is to say, a duplicate aerian and aquatic res- 

 piration. The origin of the Dog-fish remains, like 

 that of the Pishes proper, entirely unknown. Per- 

 haps we may admit, as does Dohrn, that the Marsi- 

 pobranchia have acquired their actual character- 

 istics by regression. As to the origin of the Verte- 

 brates, it is as yet totally unknown, Kowalevsky 

 deeming them descended from the Ascidians, and 

 Semper from the Annelids. 



I cannot here follow the illustrious palaeontologist 

 through the special study of the evolution of each 

 of the great orders of Vertebrates ; but I cannot 

 resist the desire to make known, or at least to 

 summarize, one of the most curious and most 

 philosophical of his works, the one relating to the 

 general line of "evolution of the Vertebrates. Cope 

 analyses and examines the changes which have 

 taken place in the course of development of these 

 animals, in their circulatory, their nervous, and 

 their osteological structure. 



Starting as a simple tube in the Leptocardia, the 

 heart divides itself into two cavities in the Marsipo- 

 branchia and the Fishes, into three in the Reptiles 

 and the Batrachians, and into four in the Birds and 

 Mammals. The arcs of the aorta amount to 

 numerous pairs in the Leptocardia, are reduced to 

 seven in the Marsipobranchia, to five in the Fishes, 

 to four or three in the Batrachians (at which point 

 their branchial function generally stops), to two 

 and one in the Reptiles, to a single one on the right 

 side, in the Birds, and to one on the left side in the 



